Obviously, you're not allowed to use trademarked characters like Superman or Batman in your published works. If I wrote a novel about Superman fighting Lex Luthor, I could get sued.

But what about referencing those characters in a real-world context? If I wrote a book about a child fighting to survive cancer and his family using Superman as a central role model to motivate him, would that similarly break the trademark? What about a book that has nothing to do with Superman or Batman, but which features a scene where two friends casually discuss which superhero would win in a fight?

Is there a distinction between "using" a trademarked character and "referencing" that same character? If so, what is the dividing line?

UPDATE: Thanks to a very helpful comment, I've edited my post to change "copyright" to "trademark." I'd still love for someone to help me navigate the possible repercussions, though!

Actually, you can't copyright a character. You can only trademark them. (...and in this case I can't help you. While I understand Copyright with its Fair Use pretty well, Trademark Law is utter mess, including paradoxes like people forbidden to use their own names, or trademarking a color.)
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SF.Dec 6 '13 at 0:34

@SF Actually, characters can be subject to copyright, as well. If you wrote a novel with the characters from the Harry Potter series, for example, by using the same descriptions and distinctive elements (even if you call them different names), that would be an infringement (Parody would be an exception to this)
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Cliff Hangerson PageDec 6 '13 at 15:05